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Preperitoneal pocket construction
- A midline incision is made extending from the sternal
notch to the umbilicus with division of the linea alba.
- Sternotomy is performed prior to creation of the pocket
in order to have quick access to the heart in the event
of hemodynamic instability.
- The preperitoneal fat is dissected from the undersurface
of the rectus sheath using low power cautery. Superiorly
the dissection is carried to the undersurface of the
diaphragm until the apex of the heart can be palpated
just lateral to the inferior phrenic artery and vein.
These vessels should be ligated to avoid injury during
transdiaphragmatic placement of the inflow cannula,
as bleeding from this site is difficult to visualize
after device insertion. If the peritoneum is entered
during the dissection, the defect is repaired with prolene
sutures to prevent herniation of abdominal contents.
If the desired plane is difficult to develop, the rectus
sheath can be entered and the posterior sheath left
as a patch overlying the peritoneum.
- This dissection must be carried well back into the
retroperitoneum (posterior to the spleen) to allow adequate
mobilization to fit the device preperitoneally
- A plastic model of the device can be inserted into
the pocket to assess whether enough room is available
for the device.
- The preperitoneal space to the right of the linea alba
is also opened for about 2 to 3 cm to facilitate closure
of the linea alba at the completion of the case and
allow room for the device outflow valve and graft conduit.
- The muscular attachment of the right hemidiaphragm
to the medial edge of the sternum must also be divided
to allow room for the graft.
Driveline tunnel creation
- The driveline usually exits in the right lower quadrant,
approximately at McBurney's point.
- A small incision is made (approx. 85% of the driveline
diameter), and a tunneling device passed subcutaneously
inferiorly around the umbilicus, and then into the pocket
through the rectus sheath at it's most inferior aspect.
This entry point into the pocket should later be examined
to make sure there is no bleeding from the rectus muscle
or an arterial branch. The tunneler is then screwed
onto the end of the driveline, which is then pulled
back through the tunnel to the skin.
- The drive line is not sutured or otherwise
attached to the skin.
Attaching the apical cuff and transdiaphragmatic passage
of the inflow cannula
- A standard dose of Heparin is given and cardiopulmonary
bypass instituted using standard aortic and dual stage
venous cannulae. The aorta is not crossclamped although
it can be.
- The apex of the left ventricle is elevated.
- There are two approaches that can be used at this juncture:
1) the apical cuff sutures are placed first and then
the myocardium cored out or 2) the hole is first made
with the coring device and then the apical cuff sutures
placed.
- An apical vent is passed into the left ventricle.
The apical vent will serve as the center of the
sight of insertion of the apical cuff. Pledgeted
2-0 ethibond sutures are placed circumferentially
partial thickness into the myocardium then passed
through the sewing ring of the apical cuff. The
coring device is then used to cut a hole in the
myocardium and the sutures are secured.
- If necessary the heart can be vented through
the right superior pulmonary vein. The coring
device is used to make the hole in the apex. This
technique is particularly useful if there is ventricular
thrombus or the myocardium is friable from recent
infarction.
- To core the apical hole the ventricle is distended
and the coring knife is aimed towards the lateral wall
to avoid entering or positioning the inflow cannula
towards the septum. Residual muscle or scar that may
impinge on the cannula site is resected. A search for
loose mural thrombus is made, adherent thrombus is left
in place.
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- For either method it is important to ensure that more
myocardium is gathered at the perimeter of the sewing
circle than at its center. These sutures are deep but
not full thickness. If a coronary vessel is lacerated,
the next suture should incorporate the bleeding site,
as it is very difficult to visualize this area once
the device has been attached.
- Once the apical cuff is secure, a cruciate incision
in the diaphragm opposite the ventricular apex is made
just lateral to the inferior phrenic vessels, and the
device inflow cannula is brought into the chest. The
inflow cannula is then inserted through the apical cuff
until the entire sintered titanium surface is within
the cuff. The surgeon should aim the cannula away from
the interventricular septum to prevent inflow restriction
aspiration of the ventricular septal muscle into the
cannula. The dacron tie of the inflow cuff is then secured
and an additional plastic band and dacron tie used to
reinforce the connection and flatten out the silicone
cuff to minimize the risk of aspirating air into the
device. Blood is now allowed to passively fill the device
and exit via the outflow valve, serving as a vent and
de-airing the device.
Anastamosis of the outflow graft to the ascending aorta
- A partial occluding clamp is placed on the right lateral
aspect of the ascending aorta and a longitudinal aortotomy
performed. The periaortic adventitia is left in place,
and a strip of bovine or native pericardium incorporated
into the anastomosis.
- The outflow graft is usually cut to a length of 12
to 15 cm. If too long the graft will kink as the chest
is closed. Finally the connector from the outflow graft
is inspected for thrombus and cleaned.
- If the outflow graft is not attached to the housing
of the pump already, make sure the nut to secure it
has been placed on the graft prior to anastamosis to
the aorta.
- The anastamosis is created with 4-0 Prolene suture.
The apex and heel of the anastamosis are reinforced
with interrupted 4-0 prolene pledgeted horizontal mattress
stitches. These are common sites of postoperative bleeding.
- The outflow graft connector should be clean and free
of thrombus. Thrombus can interfere with the creation
of a water-tight seal and lead to significant hemorrhage.
Bleeding from this connector can be treated by wrapping
the entire connector circumferentially with a strip
of bovine pericardium, and securing it at multiple sites
with heavy silk ties to tamponade the leak.
De-airing the pump
- Large pockets of air are retained in the pump during
implant and must be removed prior to initiating complete
support.
- Components of the de-airing process include:
- Placing the patient in steep Trendelenburg position
- Volume loading, ventilation and the reduction
of CPB flow to move air from the lungs and pump
to site of egress.
- Sights for air to escape include
- a purposely loose outflow graft connection
- an 18 gauge needle placed in the outflow
graft at its highest point
- a 14 gauge ascending aortic root cannula
placed to suction
- A vascular clamp remains on the outflow graft
distally. The pump is hand cranked. The housing
of the pump is shaken repeatedly to release air.
de-airing is continued until no air is seen by
TEE and no air exits through the de-airing sites
on the outflow graft.
- The outflow connector is tightly screwed together
and secured with the heavy ethibond suture supplied
with the Heartmate. The 18 gauge needle is removed
from the graft and its insertion site closed with
a 4-0 prolene.
Starting the pump and weaning from cardiopulmonary bypass
- The field is flooded with saline to prevent aspiration
of air through the inflow valved conduit and connector
in the case of inadequate pump filling.
- Inotropic support is started before separating from
bypass and activating the LVAD. Dobutamine and milrinone
are useful inotropes particularly in the presence of
pulmonary hypertension, norepinephrine and vasopressing
are added to maintain a mean blood pressure greater
than 65 mmHg.
- Bypass flow is decreased to 2 L/min, the heart filled
with volume and the device started in the fixed mode
at 20 cycles per minute. If filling is adequate the
rate is increased as cardiopulmonary bypass flow is
reduced. The device switched to automatic mode after
the cessation of cardiopulmonary bypass.
- Transesophageal echocardiography is used to ensure
adequate ventricular decompression with bowing of the
septum away from the right ventricle. A bubble study
is also performed to rule out a patent foramen ovale,
which can result in severe hypoxemia due to a right
to left shunt.
- A thermodilution cardiac output is performed and compared
to the output from the LVAD. A difference of greater
20% between the right heart output and the measured
device output signifies significant aortic regurgitation,
which will need to be addressed, by either sewing the
noncoronary and right coronary valve leaflets together
or oversewing the valve completely.
- Protamine is given and clotting factors used as needed.
In the presence of severe coagulopathy the chest may
need to be packed open.
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